Employee Benefit Plans (Assets Measured at NAV) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Assets Category:
Fair Value	$ 318.6	$ 292.5
NAV [Member]
Assets Category:
Fair Value	$ 314.7	287.2
Fixed Income [Member] \| United Kingdom Pension Plans [Member]
Assets Category:
Weighted average maturity period	5 years
Commingled Pools / Collective Trusts [Member] \| U.S. Equity [Member]
Assets Category:
Fair Value	$ 34.7	$ 69.5
Redemption Frequency (if currently eligible)	Daily	Daily
Redemption Notice Period	5 days	5 days
Commingled Pools / Collective Trusts [Member] \| International Equity [Member]
Assets Category:
Fair Value	$ 42.2	$ 47.6
Redemption Frequency (if currently eligible)	Daily	Daily
Redemption Notice Period	5 days	5 days
Commingled Pools / Collective Trusts [Member] \| Fixed Income [Member]
Assets Category:
Fair Value	$ 197.9	$ 134.9
Redemption Frequency (if currently eligible)	Daily	Daily
Balanced pension trusts [Member] \| International Equity [Member]
Assets Category:
Fair Value	$ 4.6	$ 4.7
Redemption Frequency (if currently eligible)	Daily	Daily
Balanced pension trusts [Member] \| Fixed Income [Member]
Assets Category:
Fair Value	$ 13.6	$ 11.9
Redemption Frequency (if currently eligible)	Daily	Daily
Pension Funds [Member] \| International Equity [Member]
Assets Category:
Fair Value	$ 3.3	$ 13.5
Redemption Frequency (if currently eligible)	Daily	Daily
Pension Funds [Member] \| Fixed Income [Member]
Assets Category:
Fair Value	$ 5.9	$ 5.1
Redemption Frequency (if currently eligible)	Daily	Daily
Pension Fund Member \| Fixed Income [Member]
Assets Category:
Fair Value	$ 5.9	$ 5.1
Pension Fund Member \| Blend [Domain]
Assets Category:
Fair Value	$ 12.5
Minimum [Member] \| Commingled Pools / Collective Trusts [Member] \| Fixed Income [Member]
Assets Category:
Redemption Notice Period	5 years	5 years
Minimum [Member] \| Balanced pension trusts [Member] \| International Equity [Member]
Assets Category:
Redemption Notice Period	3 days	3 days
Minimum [Member] \| Balanced pension trusts [Member] \| Fixed Income [Member]
Assets Category:
Redemption Notice Period	3 days	3 days
Minimum [Member] \| Pension Funds [Member] \| International Equity [Member]
Assets Category:
Redemption Notice Period	1 day	1 day
Minimum [Member] \| Pension Funds [Member] \| Fixed Income [Member]
Assets Category:
Redemption Notice Period	1 day	1 day
Maximum [Member] \| Commingled Pools / Collective Trusts [Member] \| Fixed Income [Member]
Assets Category:
Redemption Notice Period	15 days	15 days
Maximum [Member] \| Balanced pension trusts [Member] \| International Equity [Member]
Assets Category:
Redemption Notice Period	5 years	5 years
Maximum [Member] \| Balanced pension trusts [Member] \| Fixed Income [Member]
Assets Category:
Redemption Notice Period	5 years	5 years
Maximum [Member] \| Pension Funds [Member] \| International Equity [Member]
Assets Category:
Redemption Notice Period	7 days	7 days
Maximum [Member] \| Pension Funds [Member] \| Fixed Income [Member]
Assets Category:
Redemption Notice Period	7 days	7 days
Fair Value, Inputs, Level 2 [Member]
Assets Category:
Fair Value	$ 314.7	$ 287.2
Fair Value, Inputs, Level 2 [Member] \| Commingled Pools / Collective Trusts [Member] \| Fixed Income [Member]
Assets Category:
Fair Value	197.9	134.9
Fair Value, Inputs, Level 2 [Member] \| Balanced pension trusts [Member] \| Fixed Income [Member]
Assets Category:
Fair Value	13.6	11.9
Fair Value, Inputs, Level 2 [Member] \| Pension Fund Member \| Fixed Income [Member]
Assets Category:
Fair Value	5.9	$ 5.1
Fair Value, Inputs, Level 2 [Member] \| Pension Fund Member \| Blend [Domain]
Assets Category:
Fair Value	$ 12.5
Redemption Frequency (if currently eligible)	Daily

Defined benefit plan change in fair value of plan.

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- Definition

Weighted Average Maturity Period.

+ References

No definition available.

+ Details

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- Definition

Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

States the frequency (for example, annually, semi-annually, quarterly) with which the entity can redeem its investment, or portion thereof, for each of those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments), by major category.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258

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- Definition

Notice period the entity is required to deliver before it can redeem an investment calculated using net asset value per share, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but is not limited to, investments calculated by per unit, per membership interest, other equity or ownership interest and alternative investments.

+ References

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